Extended titanium dioxide pigment



Patented Aug. 10, 1943 EXTENDED TIT PIGME Andrew T. McCord and Harold F. Saunders,

Haddonfield, N, J., assignors to The Sherwin- Williams Company, Cleveland, Ohio, a company of Ohio No Drawing.

'7 Claims.

This invention relates to titanium extended pigments comprising titanium dioxide and calcium'sulphate, and this application is a continuation in part of our copending application Serial No. 370,486, filed December 17, 1940. V

The conversion of suitabl calcium compounds to calcium sulphate of the anhydrite crystalline form by the action of strong sulphuric acid is well known. Calcium oxide, hydroxide, carbonate, or any other compound which will be converted into a sulphate by the sulphuric acid present, may be employed. The quantity of acid taken must be sufficient to react according to the equation CaO+H2SO4=CaSO4+HzQ and an excess is desirable. The strength of the acid must be sufficiently high to effect a dehydrating condition, otherwise the calcium sulphate will be in the gypsum rather than the anhydrite form, and the temperature of the reaction must be such that complete conversion tothe anhydrite form results. The relations of concentration of acid, time, and temperature of treatment are well 88? tablished.

In our copending application, Serial No. 370,- 486, of which the present application is a continuation in part, it was disclosed that if the anhydrite form of calcium sulphate be produced by the action of strong sulphuric acid on a calcium compound other than-the sulphate, but capable of being converted to the sulphate by reaction with sulphuric acid, and that during the reaction and conversion of such calcium compound to anhydrite there is present a suitable titanium compound, the resulting anhydrite will be an improvement over that obtained'in a similar reaction, but in the absence of the titanium compound, and will possess extreme whiteness of color, fine particle size, very soft texture, ease of mixing and dispersion in a vehicle, a definite improvement in chalk and fading resistance properties, and requiring shorter grinding time to reduce to the desired state of fineness, and be particularly well adapted for usage as an extender pigment in paints, or as a filler for paper, rubber, textiles, etc. That new product and the process of making it are claimed in that application.

One distinctive property of our new product is that when added to an ilmenite solution or other sulphuric acid solution of titanium, and the mixture thermally hydrolyzed, thev precipitate ob- Application October 23, 1942, Serial No. 463,081

tained will by calcination at between 700 and 1000 C. be converted into a pigmentary titanium dioxide of rutile structure associated with calcium sulphate 0f anhydrite form. For this reason we have termed our product activated anhydrite," and shall hereinafter refer by this term to calcium sulphate of the anhydrite crystalline structure as produced by the action of strong sulphuric acid upon a suitable calcium compound, such reaction having taken place in the presence of a suitable titanium compound, said titanium compound having been added prior to the reaction between the calcium compound and the sulphuric acid, and present during the formation of the calcium sulphate from th original calcium. By the term activation we mean the conferring upon calcium sulphate the characteristic property of effecting the precipitate of hydrous titanium oxide obtained by boiling an ilmenite solution in the presence of the activated calcium sulphate in such a manner that upon calcination it is converted into rutile rather than anatase.

No one particular form of titanium compound is necessary for the production of the activated anhydrite, and we may employ a hydrous titanium dioxide such as y-titanic acidor the precipitate obtained from mineral acid solutions of titanium by thermal hydrolysis or by reaction with an alkaline material, or w mayus a soluble titanium compound such as titanium sulphate, nitrate, chloride, or fluoride providing the compound employed will during the reaction between the calcium compound and the sulphuric acid associate itself with the calcium sulphate formed or be transformed toanother compound of'titanium associated with the calcium sulphate.

We may use the hydrous titanium dioxide Angstrom units to correspond to interplanar dis- Tfie strength of the sulphuric acid employed is not critical but must be sufliciently high that upon dilution by the addition of the aqueous slurry of the calcium compound, a dehydrating condition is retained. We prefer to usesulphuric acid of 90% concentration and a minimum of 80% con-.

centration, but a concentration somewhat lower than this may be employed providing the temperature of reaction is maintained sufficiently high. By using a 90% concentration the heat of reaction alone is sufficient to cause the batch to boil and no additional heat is necessary. As the concentration drops below 80%, addition of heat is required to complete the conversion to the anhydrite form with no gypsum present. Nevertheless, formation of anhydrite may be effected with these weaker-acids if a suspension is boiled for a suiiicient period of time.

As an example or our procedure in making activated anhydrite we set forth the following:

EXAMPLE 1 'tivated anhydrite and employing forms of titanium compound other than 'y-titanic acid and compounds of calcium other than the oxide, were disclosed in our copending application Serial No. 370,486.

In carrying out our invention, the activated calcium sulphate may be obtained in various dif ferent forms. It may be a suspension in sulphuric acid which may be used for addition to and nucleation of an ilmenite solution for the production therefrom by boiling of an extended TiOz pigment (CaSO4/TiO2) or straight TiOz, or it may be a dry activated calcium sulphate, or it may be a dry and calcined activatedv calcium sulphate. The last two have by themselves value as pigmendrive ofi the sulphuric radical and convert thetitanium hydrate into pigmentary titanium dioxide. In prior practice, the titanium content of such extended pigment has been in the form of anatase.

In application Serial No. 349,345, a method was disclosed wherein-a slurry of an extender and a titanium. hydrate in dilute sulphuric acid was 'boiled, dewatered and calcined. The specific form of hydrous titanium dioxide used therein was added as the 'y-titanic acid, and in the resulting extended pigment, the titanium is in the rutlle modification.

The invention herein claimedis based on our discovery that if the extender which is added to an ilminite solution before the latter is hydrolyzed in the presence of the extender, be of the specific type claimed in our application 370,486, and referred to as "activated anhydrite or activated calcium sulphate, the precipitate which is obtained by hydrolysis of the ilmenite solution in ,the presence ofsuch specific extender will, after separating, washing and calcining, have its'titanium content of the rutlle modification. The product is of unusual whiteness, brightness and fine texture, and possesses a hiding power markedly higher than the similar products of the prior art. Such extended pigment has been made according to the following examples, using activated anhydrite prepared in any of the ways hereinbefore described, and with equivalent results. In the following examples, the activated anhydrite may be made by any of the procedures hereinbefore described or referred to, and therefore the following examples are not to be confined to any one off the specific methods of forming the activated anhydrite.

By ilmenite solution or ilmenite-sulphuric acid, solution we include any of the .usual solutions as prepared by methods of the prior art by the general process of digestion of ilmenite ore or other titanium-bearing material with strong sulphuric acid, recovering the titanium content by leaching the digestion mass, and purification or partial purification of this solution of titanium by any of the well known methods.

It is obvious that when activated anhydrite is prepared for the purpose of adding it to an ilmenite solution to produce a rutile-calcium sul- Phate pigment, the amount of the titanium compound used in the preparation of the activated anhydrite need not necessarily be limited to the smallpercentages described in our application Serial No. 370,486. Since 'y-titanic acid in itself is convertible to rutile upon calcination at 750 to 1000" C., any excess percent over the amount required to efiect activation of the anhydrite will simply be carried over into the ilmenite as additional TiOz in the mixture, such TiOa being capable of being converted to rutlle simultaneously with the T102 content of the mixture as introduced in the ilmenite solution, and we hold the use of greater quantities of T10: than shown in the examples for the preparation of activated anhydrite as being within the scope of this invention.

EXAMPLE 2.-TiOz-e:ctended pigment (70% CaSOa/30% TiOz) A quantity of the sulphuric acid suspension of activated anhydrite obtained by the method of Example 1, and adjusted to contain 245 grams of CaSO4, 210 grams of H2804, and 966 grams of water, was added to 1150 grams of ilmenite solution containing 8.1% T102, 20.2% H2504, and 13.85% FeSO The H2804 is both that which is free and that which is combined with titanium, but does not include that combined with the iron. The mixture was then boiled for 8 hours, by which time about 95% of the titanium was precipitated. The solids were separated and washed until the filtrate was substantially free from iron. The washing removes a small amount of CaSO4,

leaving a product which then contained approximately 70 parts of CaSO and 30 parts TiOz. The

cake was dewatered to about 45% solids and the moist cake calcined 2 hours at 975 C. The titanium in the product was all in thecrystalline form of rutile.

The calcination above referred to was performed in the laboratory. In a rotary calciner,

-a lower temperature of about 875 to 900 C. would be employed, according to the factor of calciner operation difference. The range of calcination may be stated as 750 to 1000" C.

It has been found advantageous to treat the moist cake prior to calcination with a compound of a metal of the second group of the periodic table as described in application Serial No. 367,- 390, since this treatment reduces the temperature and time required in calcination to effect proper development of crystallinity, hiding power, and other desirable pigmentary properties. An exam- .ple of a procedure including such treatment is as follows:

EXAMPLE 3.Ti0z extended pigment (70% Cesar/% TiQa) Into the moist cake in Example 2 and prior to calcination, was incorporated 0.2% of MgO based on the total solids in the form of MgSOi previously dissolved in a little water. This cake was then calcined for 4 hours at 900 C.

EXAMPLE 4Tz '0z extended pigment (30% CaSO4/70% TiOz) The precipitate from Example 4 was washed for a sufiicient time to remove substantially all of the 02504, dewatered, and the moist cake mixed with 0.2% ZnO (based on T102), as a solution of zinc sulphate. Caloination for 2 hours at 950 C. produced a pigmentary rutile practically 100% Ti02.

EXAMPLE 6.-Use of large proportion of TiOz in making the activated anhydrite To 421 grams of 90% sulphuric acid was added a quantity of 'y-titanic acid equivalent to 40 grams T102, and after the solids had dispersed 100 grams ofcalcium oxide in 900 grams of waterwas slowly added as a slurry with good agitation. The heat reaction caused the mixture to boil. The lime slurry was added in 30 minutes. The resulting slurry consisted of a suspension of activated anhydrite and titania hydrate in sulphuric acid. Microscopic examination disclosed the complete absence of gypsum. To the slurry was'added 626 grams of an ilmenite solution containing 85% T102, 21.4% H2504 and 14.1% F6504. The mixture was boiled for 3 hours, by which time the sample of filtrate contained 3.9 g./l. T102.

The solids were separated and washed until substantially free from iron, using approximately 5 times the original volume of wash water.

The dewatered cake was calcined for 2 hours at 975 C. to produce a product containing ap proximately 30% rutile and 70% anhydrite.

The examples put forth are typical and may be considered suificient to disclose the process. It is to be understood that any of the activated anhydrites may be used in place of the particular one of Example 1. It is also to be understood that the examples above representing 70/30 ratio CaSOr/TiOa are only representative, as ratios of TiOz from 1 up to 100 are within the scope of the practice of this invention.

The following tabulation demonstrates the superiorities of our pigment.

Tinting strength determined by the A. S. T. M. procedure D-332-36 70/30 CaSm/anatase pigment by prior art (high grade commercially available 7 pigments) 70/30 pigment from anhydrite activated with -titanic acid as per Examples 2 and 3 610 70/30 pigments from various activated anhydrites 550-640 Hiding power Hiding power-as square feet per pound of pigment was determined according to A. S. T. M.

Designation D-406-39, on the prior art pigments, and shows 48 square feet, while our products showed from to square feet.

Color A direct visual comparison in oil shows ours product to be equal or superior to the highest grade /30 CaSOr anatase extended pigments available, and to possess a superior retention of color on exposure to atmospheric condition in paint film.

Because of the greater hiding power, further extension of rutile pigmentsin paint formulation is possible with our pigments, to obtain hiding power equal to prior art pigments. Besides economy, another advantage of this lies in ability i prior art pigment with the improved results in secured by the use of less pigment, the diflerence in weight being compensated by addition oi a low priced extender pigment.

Having thus described our invention, what we claim as new and desire to secure by Letter Patentis:

1. The process of forming an extended pigment composed essentially oi. titanium oxide in the rutile form and calcium sulphate in the anhydrite form, which includes boiling an i'lmenite sulphuric acid solution containing a suspension of activated anhydrite, separating the solids from the liquid and calcining them at a temperature of 750 to 1,000 C.

2. The process of forming an extended pigment composed essentially of titanium oxide in the rutile form and calcium sulphate in the anhydrite form, which includes boiling an ilmenite sulphuric acid solution containing a suspension of activated anhydritc, separating the solids from the liquid, washing the solids free of iron, and calcining.

3. The process of forming an extended pigment composed essentially of titanium in the rutile form and calcium sulphate in the anhydrite form, which includes boiling an ilmenite sulphuric acid solution containing a suspension of activated anhydrite, separating the solids from the liquid, adding a small amount of a compound of a metal of group 1112 of the periodic table, and calcining. a

4. As a new rutile pigmentary composition, a product identicalwith that obtained by the process defined in claim 1. I i

5. As a new rutile pigmentary composition, a product identical with that obtained by the process defined in claim 2.

6. As a new rutile pigmentary composition, a product identical with that obtained by the process defined in claim 3.

7. The process of forming a pigment containing titanium dioxide in the rutile form, which includes boiling an ilmenite sulphuric acid solution containing a suspension of activated anhydrite, separating the solids from the liquid, washing the solids free of iron and calcium, and calcining.

ANDREW T. McCORD. HAROLD F. SAUNDERS. 

